1. Field of the Invention
The present invention relates to an electromagnetic circuit to be used for driving a pendulum or the like.
2. Description of the Prior Art
A drive circuit for detecting and driving the pendulum of a clock with one coil is shown, for example, in FIG. 4. The operations of this drive circuit will be described in the following. As the permanent magnet M of a pendulum approaches a coil L.sub.2, as shown in FIG. 5A, this coil L.sub.2 induces a voltage V.sub.1 (as shown in FIG. 6A) in a direction to repulse the magnet M. When the coil L.sub.2 comes to face the magnet M, as shown in FIG. 5B, it induces no voltage. As the coil L.sub.2 leaves the magnet M, as shown in FIG. 5C, it induces a voltage V.sub.2 (as shown in FIG. 6A) in a direction to attract the magnet M.
The voltages thus induced are generated at a terminal P of FIG. 4. If the induced voltage exceeds a reference voltage v.sub.r, a transistor T.sub.2 is turned off whereas a transistor T.sub.1 is turned on so that a drive current flows in the coil L.sub.2. The ON time t.sub.4 of this transistor T.sub.1 is determined by a capacitor C and a resistor R.sub.1.
In order to drive the magnet M efficiently, it is preferable in the case of attraction drive that the magnet M be driven at the timing of FIG. 5A, i.e., at the maximal point of the induced voltage V.sub.1, as shown in FIG. 6A. In order to satisfy this condition, therefore, the reference voltage v.sub.r and the drive time t.sub.4 are properly set.
In case the pendulum is to be driven, the drive timing and time are ordinarily different depending upon the length of the pendulum rod or the magnitude of its swing angle.
In the circuit described above, however, the drive time is uniquely determined by the time constant which in turn is determined by the capacitor C and the resistor R.sub.1. This makes it necessary to adjust the time constant each time in accordance with the length or swing angle of the pendulum rod.
In order to change the drive timing, on the other hand, the reference voltage v.sub.r has to be properly adjusted.
For example, if the swing angle is to be reduced by using the same pendulum as that of the case of FIG. 6A, the induced voltage has a reduced amplitude and a gentle change. In this case, the reference voltage v.sub.r has to be regulated to adjust the drive timing. Moreover, the drive current has to be fed to the coil for a longer time t.sub.5 than the aforementioned one at the maximal point of the induced voltage. For this necessity, the time constant of the capacitor C and the resistor R.sub.1 has to be changed.
If, in this case, the drive time is set at a larger value than that of the optimum value t.sub.4, as indicated by broken curves in FIG. 6A, for example, the swing angle grows more than necessary, and the drive current will flow, too, at the generation timing of the induced voltage V.sub.2 of opposite polarity so that it is wasted.
If, on the other hand, the drive time is set in the case of FIG. 6B at a smaller value than the optimum value t.sub.5, as indicated by broken curves, a necessary drive power may fail to be established to stop the pendulum.
Similar adjustments are also required in case the pendulum rod has a different length, followed by similar defects.
Thus, in the circuit of the prior art, both the time constant of the circuit and the reference voltage have to be adjusted each time in accordance with the magnitude of the swing angle and the length of the pendulum rod. If, moreover, these adjustments are mistaken, the resultant defects are the waste consumption of the current and the stop of the pendulum.
A detailed description of the prior art circuit constitution is given above, but the biggest defect thereof is the incapability of integrating the circuit constitution.